1. Field of the Invention
The present invention relates to a process for brush deactivation of the microwave interactive layer of a microwave interactive laminate to reduce or eliminate the capacity of the microwave interactive layer to generate heat in response to microwave energy. The present invention also relates to brush deactivated microwave interactive films and brush deactivated microwave interactive laminates which include a brush deactivated microwave interactive layer.
2. Background of the Invention
A characteristic of microwave cooking is that the exterior of foods cooked in a microwave oven, such as breads, do not have a brown or crisp texture desired by consumers. An objective of those concerned with microwave cooking has therefore been to provide ways of browning or crisping the exterior of foods cooked in a microwave oven.
One technique developed to brown or crisp the exterior of foods during microwave cooking has been the incorporation of a microwave interactive laminate into packages that contain foods. In response to microwave energy, a microwave interactive layer of the laminate generates heat which browns or crisps the surface of food.
Typically, a microwave interactive laminate includes a thin film which has a microwave interactive layer of lossy material deposited onto one side of the film. The layer of material generates heat in response to microwave energy. Film with a microwave interactive layer deposited on one side is a microwave interactive film.
To form a microwave interactive laminate, the microwave interactive film is commonly bonded to a substrate with the substrate serving as a support structure. The microwave interactive layer is disposed between the film and the substrate. The laminate may subsequently be cut into a shape that approximates the shape of a particular food product or the size of a particular package.
Commercially, a microwave interactive laminate can most conveniently be cut into rectangles for use in packages. When the food product which is being heated is circular, triangular or some other shape which does not conform to a rectangle, heat-generating areas of the microwave interactive laminate will not be covered by the food product. The exposed areas of conventional microwave interactive laminate can produce excessive heat which can scorch the food or the container. Also, the efficiency of the microwave interactive laminate is diminished when heat-generating areas are not covered by the food product since the exposed heat-generating areas absorb microwave radiation that would otherwise brown or crisp the food.
In addition, the heat-generating areas of a microwave interactive laminate can overlap each other when a package is assembled. A consequence of such an overlap is that excessive heat, which can scorch the package, is generated at the areas of overlap.
Finally, in packages where the microwave interactive laminate covers only a portion of a package or container, adhesive used to bond the microwave interactive laminate to the package or container can extend outside the area covered by the microwave interactive laminate. Adhesive outside the area of a package surface covered by the microwave interactive laminate can cause packages to stick together during production and handling.
U.S. Pat. Nos. 4,398,994 and 4,552,614 both to Beckett disclose continuous methods for forming decorative patterns of a metallized film and the use of such films in packaging. Both methods involve removing selected portions of a metal layer which has been deposited on a strip of polymer film. The '614 patent provides that the metallized surface is overprinted with an etchant-resistant material. The thus overprinted film is exposed to jets of aqueous etchant solution which is then washed. A scraper is provided to assist in the removal of etched metal and the spent etchant solution from the surface of the film.
While the foregoing apparatuses and methods of the prior art do succeed in producing a de-metalized film, they employ caustic chemicals in a complex washing and drying process. In addition, the methods and apparatus disclosed in the prior art apply to the producing of decorative metallized films, not to the production of microwave interactive laminates.